draft-ietf-mboned-mtrace-v2-07.txt   draft-ietf-mboned-mtrace-v2-08.txt 
MBONED Working Group H. Asaeda MBONED Working Group H. Asaeda
Internet-Draft Keio University Internet-Draft Keio University
Intended status: Standards Track T. Jinmei Intended status: Standards Track T. Jinmei
Expires: January 13, 2011 ISC Expires: July 11, 2011 ISC
W. Fenner W. Fenner
Arastra, Inc. Arastra, Inc.
S. Casner S. Casner
Packet Design, Inc. Packet Design, Inc.
July 12, 2010 January 7, 2011
Mtrace Version 2: Traceroute Facility for IP Multicast Mtrace Version 2: Traceroute Facility for IP Multicast
draft-ietf-mboned-mtrace-v2-07 draft-ietf-mboned-mtrace-v2-08
Abstract Abstract
This document describes the IP multicast traceroute facility. Unlike This document describes the IP multicast traceroute facility. Unlike
unicast traceroute, multicast traceroute requires special unicast traceroute, multicast traceroute requires special
implementations on the part of routers. This specification describes implementations on the part of routers. This specification describes
the required functionality in multicast routers, as well as how the required functionality in multicast routers, as well as how
management applications can use the router functionality. management applications can use the router functionality.
Status of this Memo Status of this Memo
skipping to change at page 1, line 39 skipping to change at page 1, line 39
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This Internet-Draft will expire on January 13, 2011. This Internet-Draft will expire on July 11, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 10 4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 10 4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 10
4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 10
5. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 11 5. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 12
5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 11 5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 12
5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 11 5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 13
5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 12 5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 13
5.4. Destination Address . . . . . . . . . . . . . . . . . . . 12 5.4. Mtrace2 Client Address . . . . . . . . . . . . . . . . . . 13
5.5. Query ID: 16 bits . . . . . . . . . . . . . . . . . . . . 12 5.5. Query ID: 16 bits . . . . . . . . . . . . . . . . . . . . 13
5.6. Client Port # . . . . . . . . . . . . . . . . . . . . . . 12 5.6. Client Port # . . . . . . . . . . . . . . . . . . . . . . 13
6. IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 13 6. IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 14
6.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 14
6.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 13 6.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 14
6.3. Incoming Interface Address: 32 bits . . . . . . . . . . . 14 6.3. Incoming Interface Address: 32 bits . . . . . . . . . . . 15
6.4. Outgoing Interface Address: 32 bits . . . . . . . . . . . 14 6.4. Outgoing Interface Address: 32 bits . . . . . . . . . . . 15
6.5. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 14 6.5. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 15
6.6. Input packet count on incoming interface: 64 bits . . . . 14 6.6. Input packet count on incoming interface: 64 bits . . . . 15
6.7. Output packet count on incoming interface: 64 bits . . . . 14 6.7. Output packet count on outgoing interface: 64 bits . . . . 16
6.8. Total number of packets for this source-group pair: 64 6.8. Total number of packets for this source-group pair: 64
bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.9. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 15 6.9. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 16
6.10. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 15 6.10. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 16
6.11. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 15 6.11. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 16
6.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.13. Src Mask: 7 bits . . . . . . . . . . . . . . . . . . . . . 15 6.13. Src Mask: 7 bits . . . . . . . . . . . . . . . . . . . . . 17
6.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 16 6.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 17
7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 18 7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 19
7.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 18 7.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 19
7.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 19 7.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 20
7.3. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 19 7.3. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 20
7.4. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 19 7.4. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 20
7.5. Local Address . . . . . . . . . . . . . . . . . . . . . . 19 7.5. Local Address . . . . . . . . . . . . . . . . . . . . . . 20
7.6. Remote Address . . . . . . . . . . . . . . . . . . . . . . 19 7.6. Remote Address . . . . . . . . . . . . . . . . . . . . . . 20
7.7. Input packet count on incoming interface . . . . . . . . . 19 7.7. Input packet count on incoming interface . . . . . . . . . 20
7.8. Output packet count on incoming interface . . . . . . . . 20 7.8. Output packet count on outgoing interface . . . . . . . . 21
7.9. Total number of packets for this source-group pair . . . . 20 7.9. Total number of packets for this source-group pair . . . . 21
7.10. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 20 7.10. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 21
7.11. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 20 7.11. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 21
7.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.13. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 20 7.13. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 21
7.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 20 7.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 21
8. Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 21 8. Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 22
9. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 22 9. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Traceroute Query . . . . . . . . . . . . . . . . . . . . . 22 9.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 23
9.1.1. Packet Verification . . . . . . . . . . . . . . . . . 22 9.1.1. Packet Verification . . . . . . . . . . . . . . . . . 23
9.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 22 9.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 23
9.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . . . 22 9.1.3. Mtrace2 Query Received by Non-Supported Router . . . . 23
9.2.1. Packet Verification . . . . . . . . . . . . . . . . . 23 9.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 24
9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 23 9.2.1. Packet Verification . . . . . . . . . . . . . . . . . 24
9.3. Forwarding Mtrace2 Requests . . . . . . . . . . . . . . . 25 9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 24
9.4. Sending Mtrace2 Responses . . . . . . . . . . . . . . . . 25 9.2.3. Mtrace2 Request Received by Non-Supported Router . . . 26
9.4.1. Destination Address . . . . . . . . . . . . . . . . . 25 9.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . . 26
9.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 25 9.3.1. Destination Address . . . . . . . . . . . . . . . . . 26
9.5. Proxying Mtrace2 Queries . . . . . . . . . . . . . . . . . 25 9.3.2. Source Address . . . . . . . . . . . . . . . . . . . . 26
9.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 26 9.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 27
10. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 27 9.4.1. Destination Address . . . . . . . . . . . . . . . . . 27
10.1. Sending Mtrace2 Queries . . . . . . . . . . . . . . . . . 27 9.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 27
10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 27 9.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . . 27
10.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 27 9.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 28
10.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 27 10. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 29
10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 28 10.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 29
10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 28 10.1.1. Destination Address . . . . . . . . . . . . . . . . . 29
10.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28 10.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 29
10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 28 10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 29
10.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 28 10.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 29
10.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 28 10.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 29
10.7.4. Traceroute shorter than requested . . . . . . . . . . 28 10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 30
10.8. Continuing after an error . . . . . . . . . . . . . . . . 29 10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 30
11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 30 10.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 30
11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 30 10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 30
11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 30 10.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 30
11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 30 10.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 30
11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 30 10.7.4. Traceroute shorter than requested . . . . . . . . . . 30
11.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 10.8. Continuing after an error . . . . . . . . . . . . . . . . 31
12. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 32 11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 32
12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 32 11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 32
12.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 32 11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 32
12.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 32 11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 32
12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 33 11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 32
12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 33 11.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 12. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 34
13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 34 12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 34
13.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 34 12.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 34
14. Security Considerations . . . . . . . . . . . . . . . . . . . 35 12.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 34
14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 35 12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 35
14.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 35 12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 35
14.3. Limiting Query/Request Rates . . . . . . . . . . . . . . . 35 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 36 13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 36
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 37 13.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 36
16.1. Normative References . . . . . . . . . . . . . . . . . . . 37 14. Security Considerations . . . . . . . . . . . . . . . . . . . 37
16.2. Informative References . . . . . . . . . . . . . . . . . . 37 14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 37
14.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39 14.3. Limiting Query/Request Rates . . . . . . . . . . . . . . . 37
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 38
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
16.1. Normative References . . . . . . . . . . . . . . . . . . . 39
16.2. Informative References . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction 1. Introduction
This document specifies the multicast traceroute facility named This document specifies the multicast traceroute facility named
mtrace version 2 or mtrace2. Mtrace2 allows the tracing of an IP mtrace version 2 or mtrace2. Mtrace2 allows the tracing of an IP
multicast routing paths. Mtrace2 provides additional information multicast routing paths. Mtrace2 provides additional information
about packet rates and losses, or other diagnosis information. For about packet rates and losses, or other diagnosis information. For
instance, mtrace2 is used for the following purposes. instance, mtrace2 is used for the following purposes.
o To trace the path that a packet would take from some source to o To trace the path that a packet would take from some source to
some destination. some destination.
o To isolate packet loss problems (e.g., congestion). o To isolate packet loss problems (e.g., congestion).
o To isolate configuration problems (e.g., TTL threshold). o To isolate configuration problems (e.g., TTL threshold).
Mtrace2 consists of the client and router programs. The mtrace2 Mtrace2 consists of the client and router programs. The mtrace2
client program is invoked from somewhere in the multicast tree, on a client program is invoked from somewhere in the multicast tree, on a
host, router, or proxy such as IGMP/MLD proxy Section 9.5. The node host, router, or proxy such as IGMP/MLD proxy [8]. The node invoking
invoking the program is called the mtrace2 client. the program is called the mtrace2 client.
The mtrace2 client program creates the mtrace2 Query message, which The mtrace2 client program creates the mtrace2 Query message, which
includes a source and multicast address specified by the client, and includes a source and multicast address specified by the client, and
forwards the message to its neighbor router or proxy. This initiates forwards the message to its neighbor router or proxy. This initiates
a trace of a multicast routing path from the client toward the a trace of a multicast routing path from the client toward the
specified source, or if no source address is specified, toward a core specified source, or if no source address is specified, toward a core
router. In the case of PIM-SM [6], the core router is an RP router if such a router exists. In the case of PIM-SM [6], the core
maintaining the specified multicast address. router is an RP maintaining the specified multicast address.
When a router or proxy receives an mtrace2 Query message and has the When a router or proxy receives an mtrace2 Query message and has the
corresponding routing state regarding the source and multicast corresponding routing state regarding the source and multicast
addresses specified in the Query, the router or proxy invokes the addresses specified in the Query, the router or proxy invokes the
mtrace2 router program. The mtrace2 router program creates an mtrace2 router program. The mtrace2 router program creates an
mtrace2 Request message corresponding to the query and forwards the mtrace2 Request message corresponding to the query and forwards the
Request toward the specified source or the core router. Request toward the specified source or the core router.
When a first-hop router or proxy (a single hop from the source When a first-hop router or proxy (a single hop from the source
specified in the request) or the core router receives an mtrace2 specified in the request) or the core router receives an mtrace2
Query or Request message, the router or proxy invokes the mtrace2 Query or Request message, the router or proxy invokes the mtrace2
router program. The mtrace2 router program creates an mtrace2 router program. The mtrace2 router program creates an mtrace2 Reply
Response message. The Response message is forwarded to the mtrace2 message. The Reply message is forwarded to the mtrace2 client, thus
client, thus completing the mtrace2 request. completing the mtrace2 Request.
The mtrace2 client program waits for the mtrace2 Response message and The mtrace2 client program waits for the mtrace2 Reply message and
displays the results. When an mtrace2 Response message does not come displays the results. When an mtrace2 Reply message does not come
due to network congestion, a broken router (see Section 10.6) or a due to network congestion, a broken router (see Section 10.6) or a
non-responding router (see Section 10.8), the mtrace2 client program non-responding router (see Section 10.8), the mtrace2 client program
can resend an mtrace2 Query with the lower hop count and repeat the can resend an mtrace2 Query with a lower hop count (see Section 5.1)
process until it receives an mtrace2 Response message. and repeat the process until it receives an mtrace2 Reply message.
The mtrace2 client should also be aware that the mtrace2 Query may The mtrace2 client should also be aware that the mtrace2 Query may
follow the control path on the routers. It happens when the last-hop follow the control path on the routers, in the case of a router's
or intermediate router's control plane and forwarding plane are not control plane and forwarding plane are not synchronized, e.g., a
synchronized. In this case, mtrace2 Requests will be forwarded buggy implementation. In this case, mtrace2 Requests will be
toward the specified source or the core router because the router forwarded toward the specified source or the core router because the
does not have any forwarding state for the query. router does not have any forwarding state for the query.
The mtrace2 supports both IPv4 and IPv6 multicast traceroute The mtrace2 supports both IPv4 and IPv6 multicast traceroute
facility. The protocol design, concept, and program behavior are facility. The protocol design, concept, and program behavior are
same between IPv4 and IPv6 mtrace2. While the original IPv4 same between IPv4 and IPv6 mtrace2. While the original IPv4
multicast traceroute, mtrace, the query and response messages are multicast traceroute, mtrace, the query and response messages are
implemented as IGMP messages [10], all mtrace2 messages are carried implemented as IGMP messages [10], all mtrace2 messages are carried
on UDP. The packet formats of IPv4 and IPv6 mtrace2 are different on UDP. The packet formats of IPv4 and IPv6 mtrace2 are different
because of the different address families, but the syntax is similar. because of the different address families, but the syntax is similar.
2. Terminology 2. Terminology
skipping to change at page 8, line 22 skipping to change at page 8, line 22
data flow, we refer to "upstream" and "downstream" with respect to data flow, we refer to "upstream" and "downstream" with respect to
data, unless explicitly specified. data, unless explicitly specified.
Incoming interface: Incoming interface:
The interface on which traffic is expected from the specified source The interface on which traffic is expected from the specified source
and group. and group.
Outgoing interface: Outgoing interface:
The interface on which traffic is forwarded from the specified source The interface on which traffic is forwarded from the specified source
and group toward the destination. It is the interface on which the and group toward the destination. It is the interface on which the
multicast traceroute Request was received. mtrace2 Query or Request was received.
Previous-hop router: Previous-hop router:
The router that is on the link attached to the Incoming Interface and The router that is on the link attached to the Incoming interface and
is responsible for forwarding traffic for the specified source and is responsible for forwarding traffic for the specified source and
group. group.
Last-hop router:
The router that is on the link attached to the Outgoing interface and
receives the mtrace2 Query from the adjacent mtrace2 client.
Group state: Group state:
It is the state in which a shared-tree protocol (e.g., PIM-SM [6]) It is the state in which a shared-tree protocol (e.g., PIM-SM [6])
running on a router chooses the previous-hop router toward the core running on a router chooses the previous-hop router toward the core
router or Rendezvous Point (RP) as its parent router. In this state, router or Rendezvous Point (RP) as its parent router. In this state,
source-specific state is not available for the corresponding source-specific state is not available for the corresponding
multicast address on the router. multicast address on the router.
Source-specific state: Source-specific state:
It is the state in which a routing protocol running on a router It is the state in which a routing protocol running on a router
chooses the path that would be followed for a source-specific join. chooses the path that would be followed for a source-specific join.
ALL-[protocol]-ROUTERS.MCAST.NET: ALL-[protocol]-ROUTERS.MCAST.NET:
It is a dedicated multicast address for a multicast router to It is a dedicated multicast address for a multicast router to
communicate with other routers that are working with the same routing communicate with other routers that are working with the same routing
protocol. For instance,the address of ALL-PIM-ROUTERS.MCAST.NET is protocol. For instance, the address of ALL-PIM-ROUTERS.MCAST.NET [6]
'224.0.0.13' for IPv4 and 'ff02::d' for IPv6. is '224.0.0.13' for IPv4 and 'ff02::d' for IPv6.
3. Overview 3. Overview
Given a multicast distribution tree, tracing from a source to a Given a multicast distribution tree, tracing from a source to a
multicast destination is hard, since you don't know down which branch multicast destination is hard, since you do not know down which
of the multicast tree the destination lies. This means that you have branch of the multicast tree the destination lies. This means that
to flood the whole tree to find the path from one source to one you have to flood the whole tree to find the path from one source to
destination. However, walking up the tree from destination to source one destination. However, walking up the tree from destination to
is easy, as most existing multicast routing protocols know the source is easy, as most existing multicast routing protocols know the
previous hop for each source. Tracing from destination to source can previous hop for each source. Tracing from destination to source can
involve only routers on the direct path. involve only routers on the direct path.
The party requesting the traceroute sends a traceroute Query packet The party requesting the multicast traceroute sends a traceroute
to the last-hop multicast router for the given multicast address. Query packet to the last-hop multicast router for the given multicast
The last-hop router turns the Query into a Request packet by adding a address. The last-hop router turns the Query into a Request packet
response data block containing its interface addresses and packet by changing the packet type and adding a response data block
statistics, and then forwards the Request packet via unicast to the containing its interface addresses and packet statistics, and then
router that it believes is the proper previous hop for the given forwards the Request packet via unicast to the router that the last-
source and group. Each hop adds its response data to the end of the hop router believes is the proper previous hop for the given source
Request packet, then unicast forwards it to the previous hop. The and group. Each hop adds its response data to the end of the Request
first-hop router (the router that believes that packets from the packet, then unicast forwards it to the previous hop. The first-hop
source originate on one of its directly connected networks) changes router (the router that believes that packets from the source
the packet type to indicate a Response packet and sends the completed originate on one of its directly connected networks) changes the
response to the response destination address. The response may be packet type to indicate a Reply packet and sends the completed Reply
returned before reaching the first-hop router if a fatal error to the mtrace2 client address specified in the Query header. The
condition such as "no route" is encountered along the path. Reply may be returned before reaching the first-hop router if a fatal
error condition such as "no route" is encountered along the path or
hop count is exceeded.
Multicast traceroute uses any information available to it in the Multicast traceroute uses any information available to it in the
router to attempt to determine a previous hop to forward the trace router to attempt to determine a previous hop to forward the trace
towards. Multicast routing protocols vary in the type and amount of towards. Multicast routing protocols vary in the type and amount of
state they keep; multicast traceroute endeavors to work with all of state they keep; multicast traceroute endeavors to work with all of
them by using whatever is available. For example, if a PIM-SM router them by using whatever is available. For example, if a PIM-SM router
is on the (*,G) tree, it chooses the parent towards the RP as the is on the (*,G) tree, it chooses the parent towards the RP as the
previous hop. In these cases, no source/group-specific state is previous hop. In these cases, no source/group-specific state is
available, but the path may still be traced. available, but the path may still be traced.
4. Packet Formats 4. Packet Formats
The mtrace2 message is carried as a UDP packet. The destination
address of mtrace2 Query messages is either the last-hop router
unicast address or multicast address if the mtrace2 client does not
know the proper last-hop router address. The destination address of
mtrace2 Report messages is the address specified in Previous-Hop
Router Address field in the last appended mtrace2 Standard Response
Block, which is either the previous-hop router unicast address or
multicast address. Detailed in Section 9.3.
Mtrace2 message is encoded in TLV format. If an implementation Mtrace2 message is encoded in TLV format. If an implementation
receives a TLV whose length exceeds the TLV length specified in the receives a TLV whose length exceeds the TLV length specified in the
Length field, the TLV SHOULD be accepted but any additional data Length field, the TLV SHOULD be accepted but any additional data
SHOULD be ignored. SHOULD be ignored. If an implementation receives a TLV whose type
value is unknown, the mtrace2 message SHOULD be ignored and silently
dropped.
4.1. Mtrace2 TLV format 4.1. Mtrace2 TLV format
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value .... | | Type | Length | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (8 bits) Type (8 bits)
skipping to change at page 10, line 34 skipping to change at page 10, line 45
Value (variable length) Value (variable length)
4.2. Defined TLVs 4.2. Defined TLVs
The following TLV Types are defined: The following TLV Types are defined:
Code Type Code Type
====== ====================================== ====== ======================================
1 Mtrace2 Query 1 Mtrace2 Query
2 Mtrace2 Request 2 Mtrace2 Request
3 Mtrace2 Response 3 Mtrace2 Reply
4 Mtrace2 Standard Response Block 4 Mtrace2 Standard Response Block
5 Mtrace2 Augmented Response Block 5 Mtrace2 Augmented Response Block
An mtrace2 message MUST contain one Mtrace2 Query header. A An mtrace2 message MUST contain exactly one Mtrace2 Query header. A
multicast router that sends an mtrace2 Request or Response message multicast router that sends an mtrace2 Request or Reply message MUST
MAY add one mtrace2 Standard Response block to given mtrace2 message add one mtrace2 Standard Response block to given mtrace2 message but
but MUST NOT add multiple mtrace2 Standard Response blocks to it. A MUST NOT add multiple mtrace2 Standard Response blocks to it. A
multicast router that adds one mtrace2 Standard Response block to multicast router that adds one mtrace2 Standard Response block to
given mtrace2 message MAY append one or multiple Augmented Response given mtrace2 message MAY append one or multiple Augmented Response
blocks. blocks.
The type field is defined to be "0x1" and "0x2" for mtrace2 Queries The TLV type field is defined to be "0x1" and "0x2" for mtrace2
and Requests, respectively. The type field is changed to "0x3" when Queries and Requests, respectively. An mtrace2 message containing
the packet is completed and sent as a response from the first-hop the type "0x1" is an mtrace2 Query. It is sent by an mtrace2 querier
router to the querier. (i.e., an mtrace2 client). It is changed to "0x2" by the proper
last-hop router. The type field is changed to "0x3" when the packet
is completed and sent as an mtrace2 Reply from the first-hop router
to the querier.
5. Mtrace2 Query Header 5. Mtrace2 Query Header
The mtrace2 supports both IPv4 and IPv6. If the mtrace2 Query or
Reply arrives in an IPv4 packet, all addresses specified in the
mtrace2 messages must be with IPv4 addresses.
The mtrace2 message is carried as a UDP packet. The UDP source port The mtrace2 message is carried as a UDP packet. The UDP source port
is uniquely selected by the local host operating system. The UDP is uniquely selected by the local host operating system. The UDP
destination port is the IANA reserved mtrace2 port number (see destination port is the IANA reserved mtrace2 port number (see
Section 13). The UDP checksum MUST be valid in mtrace2 messages. Section 13). The UDP checksum MUST be valid in mtrace2 messages.
The mtrace2 message includes the common mtrace2 Query header as The mtrace2 message includes the common mtrace2 Query header as
follows. The header is only filled in by the originator of the follows. The header is only filled in by the originator of the
mtrace2 Query; intermediate routers MUST NOT modify any of the mtrace2 Query; intermediate routers MUST NOT modify any of the
fields. fields.
skipping to change at page 11, line 31 skipping to change at page 12, line 35
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Multicast Address | | Multicast Address |
| | | |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| | | |
| Source Address | | Source Address |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Destination Address | | Mtrace2 Client Address |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query ID | Client Port # | | Query ID | Client Port # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Figure 1
5.1. # hops: 8 bits 5.1. # hops: 8 bits
This field specifies the maximum number of hops that the mtrace2 This field specifies the maximum number of hops that the mtrace2
client wants to trace. If there is some error condition in the client wants to trace. If there is some error condition in the
middle of the path that keeps the mtrace2 request from reaching the middle of the path that prevents an mtrace2 Reply from being received
first-hop router, this field can be used to perform an expanding-ring by the client, the client issues another mtrace2 Query with the lower
search to trace the path to just before the problem. number of hops until it receives a Reply from the first-hop router.
5.2. Multicast Address 5.2. Multicast Address
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 This field specifies the 32 bits length IPv4 or 128 bits length IPv6
multicast address to be traced, or is filled with "all 1" in case of multicast address to be traced, or is filled with "all 1" in case of
IPv4 or with the unspecified address (::) in case of IPv6 if no IPv4 or with the unspecified address (::) in case of IPv6 if no
group-specific information is desired. Note that non-group-specific group-specific information is desired. Note that non-group-specific
mtrace2 MUST specify source address. mtrace2 MUST specify source address.
5.3. Source Address 5.3. Source Address
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 This field specifies the 32 bits length IPv4 or 128 bits length IPv6
address of the multicast source for the path being traced, or is address of the multicast source for the path being traced, or is
filled with "all 1" in case of IPv4 or with the unspecified address filled with "all 1" in case of IPv4 or with the unspecified address
(::) in case of IPv6 if no source-specific information such as a (::) in case of IPv6 if no source-specific information such as a
trace for RPT in PIM-SM is desired. Note that non-source-specific trace for RPT in PIM-SM is desired. Note that non-source-specific
traceroutes may not be possible with certain multicast routing traceroutes may not be possible with certain multicast routing
protocols. protocols.
5.4. Destination Address 5.4. Mtrace2 Client Address
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 This field specifies the 32 bits length IPv4 or 128 bits length IPv6
address of the mtrace2 client. The trace starts at this destination global address of the mtrace2 client. The trace starts at this
and proceeds toward the traffic source. client address and proceeds toward the traffic source.
5.5. Query ID: 16 bits 5.5. Query ID: 16 bits
This field is used as a unique identifier for this traceroute request This field is used as a unique identifier for this mtrace2 Request so
so that duplicate or delayed responses may be detected. that duplicate or delayed Replies may be detected.
5.6. Client Port # 5.6. Client Port #
Mtrace2 response is sent back to the address specified in a Mtrace2 Reply is sent back to the address specified in an Mtrace2
Destination Address field. This field specifies the UDP port number Client Address field. This field specifies the UDP port number the
the router will send Mtrace2 Response. This client port number MUST router will send Mtrace2 Reply. This client port number MUST NOT be
NOT be changed by any router. changed by any router.
6. IPv4 Mtrace2 Standard Response Block 6. IPv4 Mtrace2 Standard Response Block
Each intermediate IPv4 router in a trace path appends "response data Each intermediate IPv4 router in a trace path appends "response data
block" to the forwarded trace packet. The standard response data block" to the forwarded trace packet. The standard response data
block looks as follows. block looks as follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
skipping to change at page 13, line 48 skipping to change at page 14, line 48
| Fwd TTL | MBZ |S| Src Mask |Forwarding Code| | Fwd TTL | MBZ |S| Src Mask |Forwarding Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.1. MBZ: 8 bit 6.1. MBZ: 8 bit
Must be zeroed on transmission and ignored on reception. Must be zeroed on transmission and ignored on reception.
6.2. Query Arrival Time: 32 bits 6.2. Query Arrival Time: 32 bits
The Query Arrival Time is a 32-bit NTP timestamp specifying the The Query Arrival Time is a 32-bit NTP timestamp specifying the
arrival time of the traceroute request packet at this router. The arrival time of the mtrace2 Request packet at this router. The 32-
32-bit form of an NTP timestamp consists of the middle 32 bits of the bit form of an NTP timestamp consists of the middle 32 bits of the
full 64-bit form; that is, the low 16 bits of the integer part and full 64-bit form; that is, the low 16 bits of the integer part and
the high 16 bits of the fractional part. the high 16 bits of the fractional part.
The following formula converts from a UNIX timeval to a 32-bit NTP The following formula converts from a UNIX timeval to a 32-bit NTP
timestamp: timestamp:
query_arrival_time query_arrival_time
= (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625) = (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625)
The constant 32384 is the number of seconds from Jan 1, 1900 to Jan The constant 32384 is the number of seconds from Jan 1, 1900 to Jan
1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a 1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a
reduction of ((tv.tv_usec / 100000000) << 16). reduction of ((tv.tv_usec / 100000000) << 16).
However, mtrace2 does not require synchronizing NTP timestamp among
all routers along paths to measure one-way latency. The use of Query
Arrival Time is useful to measure the packets per second (PPS).
Suppose that a client issues two queries Q1 and Q2, and the
corresponding requests R1 and R2 arrive at router X at t1 and t2,
then the client would be able to calculate the PPS at router X by
using the packet count results at t1 and t2.
6.3. Incoming Interface Address: 32 bits 6.3. Incoming Interface Address: 32 bits
This field specifies the address of the interface on which packets This field specifies the address of the interface on which packets
from this source and group are expected to arrive, or 0 if unknown or from this source and group are expected to arrive, or 0 if unknown or
unnumbered. unnumbered.
6.4. Outgoing Interface Address: 32 bits 6.4. Outgoing Interface Address: 32 bits
This field specifies the address of the interface on which packets This field specifies the address of the interface on which packets
from this source and group flow to the specified destination, or 0 if from this source and group flow to the specified destination, or 0 if
skipping to change at page 14, line 43 skipping to change at page 16, line 5
it should be 0 if the incoming interface address is unknown or it should be 0 if the incoming interface address is unknown or
unnumbered. unnumbered.
6.6. Input packet count on incoming interface: 64 bits 6.6. Input packet count on incoming interface: 64 bits
This field contains the number of multicast packets received for all This field contains the number of multicast packets received for all
groups and sources on the incoming interface, or "all 1" if no count groups and sources on the incoming interface, or "all 1" if no count
can be reported. This counter may have the same value as can be reported. This counter may have the same value as
ifHCInMulticastPkts from the IF-MIB [12] for this interface. ifHCInMulticastPkts from the IF-MIB [12] for this interface.
6.7. Output packet count on incoming interface: 64 bits 6.7. Output packet count on outgoing interface: 64 bits
This field contains the number of multicast packets that have been This field contains the number of multicast packets that have been
transmitted or queued for transmission for all groups and sources on transmitted or queued for transmission for all groups and sources on
the outgoing interface, or "all 1" if no count can be reported. This the outgoing interface, or "all 1" if no count can be reported. This
counter may have the same value as ifHCOutMulticastPkts from the IF- counter may have the same value as ifHCOutMulticastPkts from the IF-
MIB for this interface. MIB for this interface.
6.8. Total number of packets for this source-group pair: 64 bits 6.8. Total number of packets for this source-group pair: 64 bits
This field counts the number of packets from the specified source This field counts the number of packets from the specified source
skipping to change at page 15, line 21 skipping to change at page 16, line 29
set and the Src Mask field is 63, indicating no source-specific set and the Src Mask field is 63, indicating no source-specific
state, the count is for all sources sending to this group. This state, the count is for all sources sending to this group. This
counter should have the same value as ipMcastRoutePkts from the counter should have the same value as ipMcastRoutePkts from the
IPMROUTE-STD-MIB [13] for this forwarding entry. IPMROUTE-STD-MIB [13] for this forwarding entry.
6.9. Rtg Protocol: 16 bits 6.9. Rtg Protocol: 16 bits
This field describes the routing protocol used to decide an RPF This field describes the routing protocol used to decide an RPF
interface for the requested source. This value should have the same interface for the requested source. This value should have the same
value as ipMcastRouteRtProtocol from the IPMROUTE-STD-MIB [13] for value as ipMcastRouteRtProtocol from the IPMROUTE-STD-MIB [13] for
this entry. If the router does not able to obtain this value, "all this entry. If the router is not able to obtain this value, "all 0"
0" must be specified. must be specified.
6.10. Multicast Rtg Protocol: 16 bits 6.10. Multicast Rtg Protocol: 16 bits
This field describes the multicast routing protocol in use between This field describes the multicast routing protocol in use between
this router and the previous-hop router. This value should have the this router and the previous-hop router. This value should have the
same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] for same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] for
this entry. If the router does not able to obtain this value, "all this entry. If the router does not able to obtain this value, "all
0" must be specified. 0" must be specified.
6.11. Fwd TTL: 8 bits 6.11. Fwd TTL: 8 bits
skipping to change at page 16, line 17 skipping to change at page 17, line 24
This field contains a forwarding information/error code. Section 9.2 This field contains a forwarding information/error code. Section 9.2
explains how and when the forwarding code is filled. Defined values explains how and when the forwarding code is filled. Defined values
are as follows; are as follows;
Value Name Description Value Name Description
----- -------------- ------------------------------------------- ----- -------------- -------------------------------------------
0x00 NO_ERROR No error 0x00 NO_ERROR No error
0x01 WRONG_IF Mtrace2 request arrived on an interface 0x01 WRONG_IF Mtrace2 Request arrived on an interface
to which this router would not forward for to which this router would not forward for
this source, group, destination. this source, group, destination.
0x02 PRUNE_SENT This router has sent a prune upstream which 0x02 PRUNE_SENT This router has sent a prune upstream which
applies to the source and group in the applies to the source and group in the
traceroute request. mtrace2 Request.
0x03 PRUNE_RCVD This router has stopped forwarding for this 0x03 PRUNE_RCVD This router has stopped forwarding for this
source and group in response to a request source and group in response to a request
from the next hop router. from the next hop router.
0x04 SCOPED The group is subject to administrative 0x04 SCOPED The group is subject to administrative
scoping at this hop. scoping at this hop.
0x05 NO_ROUTE This router has no route for the source or 0x05 NO_ROUTE This router has no route for the source or
group and no way to determine a potential group and no way to determine a potential
skipping to change at page 16, line 45 skipping to change at page 17, line 52
0x06 WRONG_LAST_HOP This router is not the proper last-hop 0x06 WRONG_LAST_HOP This router is not the proper last-hop
router. router.
0x07 NOT_FORWARDING This router is not forwarding this source, 0x07 NOT_FORWARDING This router is not forwarding this source,
group out the outgoing interface for an group out the outgoing interface for an
unspecified reason. unspecified reason.
0x08 REACHED_RP Reached Rendezvous Point or Core 0x08 REACHED_RP Reached Rendezvous Point or Core
0x09 RPF_IF Mtrace2 request arrived on the expected 0x09 RPF_IF Mtrace2 Request arrived on the expected
RPF interface for this source and group. RPF interface for this source and group.
0x0A NO_MULTICAST Mtrace2 request arrived on an interface 0x0A NO_MULTICAST Mtrace2 Request arrived on an interface
which is not enabled for multicast. which is not enabled for multicast.
0x0B INFO_HIDDEN One or more hops have been hidden from this 0x0B INFO_HIDDEN One or more hops have been hidden from this
trace. trace.
0x0C REACHED_GW Mtrace2 request arrived on a gateway (e.g., 0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g.,
a NAT or firewall) that hides the a NAT or firewall) that hides the
information between this router and the information between this router and the
mtrace2 querier mtrace2 querier
0x81 NO_SPACE There was not enough room to insert another 0x81 NO_SPACE There was not enough room to insert another
response data block in the packet. response data block in the packet.
0x82 OLD_ROUTER The previous-hop router does not understand 0x82 ADMIN_PROHIB Mtrace2 is administratively prohibited.
mtrace2 requests.
0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited.
Note that if a router discovers there is not enough room in a packet Note that if a router discovers there is not enough room in a packet
to insert its response, it puts the NO_SPACE error code in the to insert its response, it puts the NO_SPACE code value in the
previous router's Forwarding Code field, overwriting any error the previous router's Forwarding Code field, overwriting any error the
previous router placed there. After the router sends the response to previous router placed there. After the router sends the Reply to
the Destination Address in the header, the router continues the the Mtrace2 Client Address in the header, the router continues the
mtrace2 query by sending an mtrace2 request containing the same mtrace2 Query by sending an mtrace2 Request containing the same
mtrace2 Query header. Section 9.3 and Section 10.8 include the mtrace2 Query header. Section 9.3 and Section 10.8 include the
details. details.
The 0x80 bit of the Forwarding Code is used to indicate a fatal The 0x80 bit of the Forwarding Code is used to indicate a fatal
error. A fatal error is one where the router may know the previous error. A fatal error is one where the router may know the previous
hop but cannot forward the message to it. hop but cannot forward the message to it.
7. IPv6 Mtrace2 Standard Response Block 7. IPv6 Mtrace2 Standard Response Block
Each intermediate IPv6 router in a trace path appends "response data Each intermediate IPv6 router in a trace path appends "response data
skipping to change at page 20, line 5 skipping to change at page 21, line 5
This may be a multicast group (e.g., ALL-[protocol]- This may be a multicast group (e.g., ALL-[protocol]-
ROUTERS.MCAST.NET) if the previous hop is not known because of the ROUTERS.MCAST.NET) if the previous hop is not known because of the
workings of the multicast routing protocol. However, it should be workings of the multicast routing protocol. However, it should be
the unspecified address (::) if the incoming interface address is the unspecified address (::) if the incoming interface address is
unknown. unknown.
7.7. Input packet count on incoming interface 7.7. Input packet count on incoming interface
Same definition described in Section 6.6 Same definition described in Section 6.6
7.8. Output packet count on incoming interface 7.8. Output packet count on outgoing interface
Same definition described in Section 6.7 Same definition described in Section 6.7
7.9. Total number of packets for this source-group pair 7.9. Total number of packets for this source-group pair
This field counts the number of packets from the specified source This field counts the number of packets from the specified source
forwarded by this router to the specified group, or "all 1" if no forwarded by this router to the specified group, or "all 1" if no
count can be reported. If the S bit is set, the count is for the count can be reported. If the S bit is set, the count is for the
source network, as specified by the Src Prefix Len field. If the S source network, as specified by the Src Prefix Len field. If the S
bit is set and the Src Prefix Len field is 255, indicating no source- bit is set and the Src Prefix Len field is 255, indicating no source-
skipping to change at page 21, line 9 skipping to change at page 22, line 9
to 255 (0xff) to 255 (0xff)
7.14. Forwarding Code: 8 bits 7.14. Forwarding Code: 8 bits
Same definition described in Section 6.14 Same definition described in Section 6.14
8. Mtrace2 Augmented Response Block 8. Mtrace2 Augmented Response Block
In addition to the standard response block, a multicast router on the In addition to the standard response block, a multicast router on the
path will be able to add "augumented response block" when it sends path will be able to add "augumented response block" when it sends
the request to its upstream router or sends the response to the the mtrace2 Request to its upstream router or sends the Reply to the
Destination Address. This augmented response block is flexible to Mtrace2 Client Address. This augmented response block is flexible to
add various information. add various information.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Value .... | | Type | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The augmented response block is always appended to mtrace2 TLV header The augmented response block is always appended to mtrace2 TLV header
(0x04). The 16 bits Type filed of the augmented response block is (0x04). The 16 bits Type filed of the augmented response block is
defined for various purposes, such as diagnosis (as in Section 12) defined for various purposes, such as diagnosis (as in Section 12)
and protocol verification. The packet length of the augmented and protocol verification. The packet length of the augmented
response block is specified in the augmented response block TLV response block is specified in the augmented response block TLV
header as seen in Section 4.1. header as seen in Section 4.1.
The following augmented response block type is defined: The following augmented response block type is defined:
Code Type Code Type
====== ================================================= ====== =================================================
0x01 # Mtrace2 Standard Response Blocks Returned 0x01 # Mtrace2 Standard Response Blocks Returned
When the NO_SPACE error occurs, the router sends back the mtrace2 When the NO_SPACE error occurs, the router sends back the mtrace2
response with contained data (i.e., all appended response blocks), Reply with contained data (i.e., all appended response blocks), and
and continues the mtrace2 query by sending an mtrace2 request as will continues the mtrace2 Query by sending an mtrace2 Request as will be
be described in Section 9.3. In this mtrace2 request, the router described in Section 9.3. In this mtrace2 Request, the router
appends the augmented response block with the code "0x01" and the appends the augmented response block with the code "0x01" and the
number of returned mtrace2 response blocks. Every router between number of returned mtrace2 response blocks. Every router between
this router and the first-hop router can recognize the limit number this router and the first-hop router can recognize the limit number
of hops by referring this number and the # hops in the header. of hops by referring this number and the # hops in the header.
This document only defines the above augmented response block type This document only defines the above augmented response block type
and does not define other augmented response block types. Specifing and does not define other augmented response block types. Specifing
how to deal with diagnosis information will be also described in how to deal with diagnosis information will be also described in
separate documents. separate documents.
9. Router Behavior 9. Router Behavior
All of these actions are performed in addition to (NOT instead of) All of these actions are performed in addition to (NOT instead of)
forwarding the packet, if applicable. E.g. a multicast packet that forwarding the packet, if applicable. E.g. a multicast packet that
has TTL or the hop limit remaining MUST be forwarded normally, as has TTL or the hop limit remaining MUST be forwarded normally, as
MUST a unicast packet that has TTL or the hop limit remaining and is MUST a unicast packet that has TTL or the hop limit remaining and is
not addressed to this router. not addressed to this router.
9.1. Traceroute Query 9.1. Receiving Mtrace2 Query
An mtrace2 Query message is a traceroute message with no response An mtrace2 Query message is an mtrace2 message with no response
blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2. blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2.
9.1.1. Packet Verification 9.1.1. Packet Verification
Upon receiving an mtrace2 Query message, a router must examine the Upon receiving an mtrace2 Query message, a router must examine the
Query to see if it is the proper last-hop router for the destination Query to see if it is the proper last-hop router for the destination
address in the packet. It is the proper last-hop router if it has a address in the packet. It is the proper last-hop router if it has a
multicast-capable interface on the same subnet as the Destination multicast-capable interface on the same subnet as the Mtrace2 Client
Address and is the router that would forward traffic from the given Address and is the router that would forward traffic from the given
(S,G) onto that subnet. (S,G) or (*,G) onto that subnet.
If the router determines that it is not the proper last-hop router, If the router determines that it is not the proper last-hop router,
or it cannot make that determination, it does one of two things or it cannot make that determination, it does one of two things
depending if the Query was received via multicast or unicast. If the depending if the Query was received via multicast or unicast. If the
Query was received via multicast, then it MUST be silently dropped. Query was received via multicast, then it MUST be silently dropped.
If it was received via unicast, a forwarding code of WRONG_LAST_HOP If it was received via unicast, a forwarding code of WRONG_LAST_HOP
is noted and processing continues as in Section 9.2 is noted and processing continues as in Section 9.2.
Duplicate Query messages as identified by the tuple (IP Source, Query Duplicate Query messages as identified by the tuple (Mtrace2 Client
ID) SHOULD be ignored. This MAY be implemented using a simple 1-back Address, Query ID) SHOULD be ignored. This MAY be implemented using
cache (i.e. remembering the IP source and Query ID of the previous a simple 1-back cache (i.e. remembering the Mtrace2 Client Address
Query message that was processed, and ignoring future messages with and Query ID of the previous Query message that was processed, and
the same IP Source and Query ID). Duplicate Request messages MUST ignoring future messages with the same Mtrace2 Client Address and
NOT be ignored in this manner. Query ID). Duplicate Request messages MUST NOT be ignored in this
manner.
9.1.2. Normal Processing 9.1.2. Normal Processing
When a router receives an mtrace2 Query and it determines that it is When a router receives an mtrace2 Query and it determines that it is
the proper last-hop router, it treats it like an mtrace2 Request and the proper last-hop router, it it changes the TLV type to 0x2 and
performs the steps listed in Section 9.2 treats it like an mtrace2 Request and performs the steps listed in
Section 9.2.
9.2. Mtrace2 Request 9.1.3. Mtrace2 Query Received by Non-Supported Router
When a router that does not support mtrace2 receives an mtrace2 Query
message whose destination address is multicast, the router will
silently discard the message. When the router receives an mtrace2
Query message whose destination address is the router's interface
address, the router returns an ICMP Port unreachable to the Mtrace2
Client Address.
9.2. Receiving Mtrace2 Request
An mtrace2 Request is a traceroute message with some number of An mtrace2 Request is a traceroute message with some number of
response blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 response blocks filled in, and uses TLV type 0x2 for IPv4 and IPv6
mtrace2. Routers can tell the difference between Queries and mtrace2.
Requests by checking the length of the packet.
9.2.1. Packet Verification 9.2.1. Packet Verification
If the mtrace2 Request does not come from an adjacent host or router, If the mtrace2 Request does not come from an adjacent host or router,
it MUST be silently ignored. If the mtrace2 Request is not addressed it MUST be silently ignored. If the mtrace2 Request is not addressed
to this router, or if the Request is addressed to a multicast group to this router, or if the Request is addressed to a multicast group
which is not a link-scoped group (i.e. 224/24 for IPv4, FFx2::/16 [3] which is not a link-scoped group (i.e. 224/24 for IPv4, FFx2::/16 [3]
for IPv6), it MUST be silently ignored. GTSM [14] SHOULD be used by for IPv6), it MUST be silently ignored. GTSM [14] SHOULD be used by
the router to determine whether the host or router is adjacent or the router to determine whether the host or router is adjacent or
not. not.
skipping to change at page 23, line 29 skipping to change at page 24, line 39
by the Forwarding Codes. The first one encountered is the one that by the Forwarding Codes. The first one encountered is the one that
is reported, i.e. all "note forwarding code N" should be interpreted is reported, i.e. all "note forwarding code N" should be interpreted
as "if forwarding code is not already set, set forwarding code to N". as "if forwarding code is not already set, set forwarding code to N".
1. If there is room in the current buffer (or the router can 1. If there is room in the current buffer (or the router can
efficiently allocate more space to use), insert a new response efficiently allocate more space to use), insert a new response
block into the packet and fill in the Query Arrival Time, block into the packet and fill in the Query Arrival Time,
Outgoing Interface Address (for IPv4 mtrace2) or Outgoing Outgoing Interface Address (for IPv4 mtrace2) or Outgoing
Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd
TTL (for IPv4 mtrace2). If there was no room, fill in the TTL (for IPv4 mtrace2). If there was no room, fill in the
response code "NO_SPACE" in the *previous* hop's response block, forwarding code "NO_SPACE" in the *previous* hop's response
and forward the packet to the address specified in the block, and forward the packet to the address specified in the
Destination Address field and continue the trace as described in Mtrace2 Client Address field and continue the trace as described
Section 9.3. in Section 9.3.
2. Attempt to determine the forwarding information for the source 2. Attempt to determine the forwarding information for the source
and group specified, using the same mechanisms as would be used and group specified, using the same mechanisms as would be used
when a packet is received from the source destined for the when a packet is received from the source destined for the
group. State need not be instantiated, it can be "phantom" group. A state need not be instantiated, it can be "phantom"
state created only for the purpose of the trace, such as "dry- state created only for the purpose of the trace, such as "dry-
run". run".
If using a shared-tree protocol and there is no source-specific If using a shared-tree protocol and there is no source-specific
state, or if no source-specific information is desired (i.e., state, or if no source-specific information is desired (i.e.,
"all 1" for IPv4 or unspecified address (::) for IPv6), group "all 1" for IPv4 or unspecified address (::) for IPv6), group
state should be used. If there is no group state or no group- state should be used. If there is no group state or no group-
specific information is desired, potential source state (i.e. specific information is desired, potential source state (i.e.,
the path that would be followed for a source-specific Join) the path that would be followed for a source-specific Join)
should be used. If this router is the Core or RP and no source- should be used. If this router is the Core or RP and no source-
specific state is available (e.g., this router has been specific state is available (e.g., this router has been
receiving PIM Register messages from the first-hop router), note receiving PIM Register messages from the first-hop router), note
a code of REACHED_RP. a code of REACHED_RP.
3. If no forwarding information can be determined, the router notes 3. If no forwarding information can be determined, the router notes
an error code of NO_ROUTE, sets the remaining fields that have a forwarding code of NO_ROUTE, sets the remaining fields that
not yet been filled in to zero, and then forwards the packet to have not yet been filled in to zero, and then forwards the
the mtrace2 client as described in Section 9.3. packet to the mtrace2 client as described in Section 9.3.
4. Fill in the Incoming Interface Address, Previous-Hop Router 4. Fill in the Incoming Interface Address, Previous-Hop Router
Address, Input Packet Count, Total Number of Packets, Routing Address, Input Packet Count, Total Number of Packets, Routing
Protocol, S, and Src Mask from the forwarding information that Protocol, S, and Src Mask from the forwarding information that
was determined. was determined.
5. If mtrace2 is administratively prohibited or the previous hop 5. If mtrace2 is administratively prohibited, note the appropriate
router does not understand mtrace2 requests, note the forwarding code (ADMIN_PROHIB). If mtrace2 is administratively
appropriate forwarding code (ADMIN_PROHIB or OLD_ROUTER). If prohibited and any of the fields as filled in step 4 are
mtrace2 is administratively prohibited and any of the fields as considered private information, zero out the applicable fields.
filled in step 4 are considered private information, zero out Then the packet is forwarded to the mtrace2 client as described
the applicable fields. Then the packet is forwarded to the in Section 9.3.
mtrace2 client as described in Section 9.3.
6. If the reception interface is not enabled for multicast, note 6. If the reception interface is not enabled for multicast, note
forwarding code NO_MULTICAST. If the reception interface is the forwarding code NO_MULTICAST. If the reception interface is the
interface from which the router would expect data to arrive from interface from which the router would expect data to arrive from
the source, note forwarding code RPF_IF. Otherwise, if the the source, note forwarding code RPF_IF. Otherwise, if the
reception interface is not one to which the router would forward reception interface is not one to which the router would forward
data from the source to the group, a forwarding code of WRONG_IF data from the source to the group, a forwarding code of WRONG_IF
is noted. is noted.
7. If the group is subject to administrative scoping on either the 7. If the group is subject to administrative scoping on either the
skipping to change at page 24, line 50 skipping to change at page 26, line 10
code PRUNE_SENT. If the router has stopped forwarding code PRUNE_SENT. If the router has stopped forwarding
downstream in response to a prune sent by the next hop router, downstream in response to a prune sent by the next hop router,
it notes forwarding code PRUNE_RCVD. If the router should it notes forwarding code PRUNE_RCVD. If the router should
normally forward traffic for this source and group downstream normally forward traffic for this source and group downstream
but is not, it notes forwarding code NOT_FORWARDING. but is not, it notes forwarding code NOT_FORWARDING.
10. If this router is a gateway (e.g., a NAT or firewall) that hides 10. If this router is a gateway (e.g., a NAT or firewall) that hides
the information between this router and the mtrace2 querier, it the information between this router and the mtrace2 querier, it
notes forwarding code REACHED_GW. notes forwarding code REACHED_GW.
11. The packet is then sent on to the previous hop or the 11. The packet is then sent on to the previous hop or the Mtrace2
Destination Address as described in Section 9.3. Client Address as described in Section 9.3.
9.3. Forwarding Mtrace2 Requests 9.2.3. Mtrace2 Request Received by Non-Supported Router
If the Previous-hop router is known for this request and the number When a router that does not understand mtrace2 Request messages
of response blocks is less than the number requested (i.e., the "# receives an mtrace2 Request message whose destination address is
hops" field in mtrace2 Query header), the packet is sent to that multicast, the router will silently discard the message. When the
router. If the Incoming Interface is known but the Previous-hop router receives an mtrace2 Request message whose destination address
router is not known, the packet is sent to an appropriate multicast is the router's interface address, the router returns an ICMP Port
address on the Incoming Interface. The appropriate multicast address unreachable to the Mtrace2 Client Address, and the mtrace2 client may
may depend on the routing protocol in use, MUST be a link-scoped then issue another mtrace2 Query with the lower number of # hops.
group (i.e. 224/24 for IPv4, FF02::/16 for IPv6), MUST NOT be ALL-
SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and All Nodes Address 9.3. Forwarding Mtrace2 Request
(FF02::1) for IPv6, and MAY be ALL-ROUTERS.MCAST.NET (224.0.0.2) for
IPv4 or All Routers Address (FF02::2) for IPv6 if the routing 9.3.1. Destination Address
protocol in use does not define a more appropriate group. Otherwise,
it is sent to the Destination Address in the header. If the Previous-hop router for the mtrace2 Request is known for this
request and the number of response blocks is less than the number
requested (i.e., the "# hops" field in the mtrace2 Query header), the
packet is sent to that router. If the Incoming Interface is known
but the Previous-hop router is not known, the packet is sent to an
appropriate multicast address on the Incoming Interface. The
appropriate multicast address may depend on the routing protocol in
use, MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for
IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and All
Nodes Address (FF02::1) for IPv6, and MAY be ALL-ROUTERS.MCAST.NET
(224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6 if the
routing protocol in use does not define a more appropriate group.
Otherwise, it is sent to the Mtrace2 Client Address in the header.
9.3.2. Source Address
An mtrace2 Request should be sent with the address of the router's
reception interface. However, if the router's interface address is
unnumbered, the router can use one of its numbered interface address
as the source address.
When the REACHED_GW code is noted, the router sends back the mtrace2 When the REACHED_GW code is noted, the router sends back the mtrace2
response as in Section 9.4. In addition to that, it must continue Reply as in Section 9.4. In addition to that, it must continue the
the mtrace2 query by proxying the original querier as in Section 9.5. mtrace2 Query by proxying the original querier as in Section 9.5.
When the NO_SPACE error occurs, the router sends back the mtrace2 When the NO_SPACE error occurs, the router sends back the mtrace2
response with contained data and the NO_SPACE error code as in Reply with contained data and the NO_SPACE error code as in
Section 9.4, and continues the mtrace2 query by sending an mtrace2 Section 9.4, and continues the mtrace2 Query by sending an mtrace2
request containing the same mtrace2 Query header and its standard and Request containing the same mtrace2 Query header and its standard and
augmented response blocks. The corresponding augmented response augmented response blocks. The corresponding augmented response
block type is "# Mtrace2 Response Blocks Returned" described in block type is "# Mtrace2 Response Blocks Returned" described in
Section 8. Section 8.
9.4. Sending Mtrace2 Responses 9.4. Sending Mtrace2 Reply
9.4.1. Destination Address 9.4.1. Destination Address
An mtrace2 Response must be sent to the address specified in the An mtrace2 Reply must be sent to the address specified in the Mtrace2
Destination Address field in the mtrace2 Query header. Client Address field in the mtrace2 Query header.
9.4.2. Source Address 9.4.2. Source Address
An mtrace2 Response must be sent with the address of the router's An mtrace2 Reply should be sent with the address of the router's
reception interface. reception interface. However, if the router's interface address is
unnumbered, the router can use one of its numbered interface address
as the source address.
9.5. Proxying Mtrace2 Queries 9.5. Proxying Mtrace2 Query
When a gateway (e.g., a NAT or firewall) that needs to block unicast When a gateway (e.g., a NAT or firewall) that needs to block unicast
packets to the mtrace2 querier or hide information between the packets to the mtrace2 querier or hide information between the
gateway and the mtrace2 querier receives mtrace2 query from an gateway and the mtrace2 querier receives mtrace2 Query from an
adjacent host or mtrace2 request from an adjacent router, it sends adjacent host or mtrace2 Request from an adjacent router, it sends
back the mtrace2 response with contained data and the REACHED_GW code back the mtrace2 Reply with contained data and the REACHED_GW code to
to the address specified in the Destination Address field in the the address specified in the Mtrace2 Client Address field in the
mtrace2 Query header. mtrace2 Query header.
At the same time, the gateway prepares a new mtrace2 query message. At the same time, the gateway prepares a new mtrace2 Query message.
The gateway uses the original mtrace2 Query header as the base for The gateway uses the original mtrace2 Query header as the base for
the new mtrace2 query; it sets the Destination Address to its the new mtrace2 Query; it sets the Mtrace2 Client Address to its
Incoming Interface address and the Client Port # to its own port Incoming Interface address and the Client Port # to its own port
(which may be the same as the mtrace2 port as the gateway is (which may be the same as the mtrace2 port as the gateway is
listening on that port), and decreases # hops according to the number listening on that port), and decreases # hops according to the number
of standard response blocks in the returned mtrace2 response from the of standard response blocks in the returned mtrace2 Reply from the
gateway. The mtrace2 query message is sent to the previous-hop gateway. The mtrace2 Query message is sent to the previous-hop
router or to an appropriate multicast address on the Incoming router or to an appropriate multicast address on the Incoming
Interface. Interface.
When the gateway receives the mtrace2 response from the first-hop When the gateway receives the mtrace2 Reply from the first-hop router
router or any intermediate router, it MUST forward the mtrace2 or any intermediate router, it MUST forward the mtrace2 Reply back to
response back to the mtrace2 querier with the original mtrace2 Query the mtrace2 querier with the original mtrace2 Query header.
header.
9.6. Hiding Information 9.6. Hiding Information
Information about a domain's topology and connectivity may be hidden Information about a domain's topology and connectivity may be hidden
from multicast traceroute requests. The INFO_HIDDEN forwarding code from mtrace2 Requests. The INFO_HIDDEN forwarding code may be used
may be used to note that, for example, the incoming interface address to note that, for example, the incoming interface address and packet
and packet count are for the entrance to the domain and the outgoing count are for the entrance to the domain and the outgoing interface
interface address and packet count are the exit from the domain. The address and packet count are the exit from the domain by specifying
source-group packet count may be from either router or not specified "all 1". The source-group packet count (Section 6.8 and Section 7.9)
(all 1). is from router, but may be "all 1" if it is hidden.
10. Client Behavior 10. Client Behavior
10.1. Sending Mtrace2 Queries 10.1. Sending Mtrace2 Query
When the destination of the mtrace2 is the machine running the 10.1.1. Destination Address
client, the mtrace2 Query packet can be sent to the ALL-
ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address Mtrace2 Query packet can be sent to the ALL-ROUTERS.MCAST.NET
(FF02::2) for IPv6. This will ensure that the packet is received by (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6. This
the last-hop router on the subnet. Otherwise, if the proper last-hop will ensure that the packet is received by the last-hop router on the
router is known for the mtrace2 destination, the Query could be subnet. Otherwise, if the proper last-hop router is known for the
unicasted to that router. mtrace2 destination, the Query is unicasted to that router.
See also Section 10.4 on determining the last-hop router. See also Section 10.4 on determining the last-hop router.
10.1.2. Source Address
An mtrace2 Query must be sent with the address of the mtrace2
querier's reception interface, which would be the Mtrace2 Client
Address.
10.2. Determining the Path 10.2. Determining the Path
The client could send a small number of initial query messages with a The client could send a small number of initial query messages with a
large "# hops" field, in order to try to trace the full path. If large "# hops" field, in order to try to trace the full path. If
this attempt fails, one strategy is to perform a linear search (as this attempt fails, one strategy is to perform a linear search (as
the traditional unicast traceroute program does); set the "# hops" the traditional unicast traceroute program does); set the "# hops"
field to 1 and try to get a response, then 2, and so on. If no field to 1 and try to get a Reply, then 2, and so on. If no Reply is
response is received at a certain hop, the hop count can continue received at a certain hop, the hop count can continue past the non-
past the non-responding hop, in the hopes that further hops may responding hop, in the hopes that further hops may respond. These
respond. These attempts should continue until a user-defined timeout attempts should continue until a user-defined timeout has occurred.
has occurred.
See also Section 10.5 and Section 10.6 on receiving the results of a See also Section 10.6 on receiving the results of a trace.
trace.
10.3. Collecting Statistics 10.3. Collecting Statistics
After a client has determined that it has traced the whole path or as After a client has determined that it has traced the whole path or as
much as it can expect to (see Section 10.7), it might collect much as it can expect to (see Section 10.7), it might collect
statistics by waiting a short time and performing a second trace. If statistics by waiting a short time and performing a second trace. If
the path is the same in the two traces, statistics can be displayed the path is the same in the two traces, statistics can be displayed
as described in Section 12.3 and Section 12.4. as described in Section 12.3 and Section 12.4.
10.4. Last Hop Router 10.4. Last Hop Router
The mtrace2 querier may not know which is the last-hop router, or The mtrace2 querier may not know which is the last-hop router, or
that router may be behind a firewall that blocks unicast packets but that router may be behind a firewall that blocks unicast packets but
passes multicast packets. In these cases, the mtrace2 request should passes multicast packets. In these cases, the mtrace2 Request should
be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All
Routers Address (FF02::2) for IPv6. All routers except the correct Routers Address (FF02::2) for IPv6. All routers except the correct
last-hop router should ignore any mtrace2 request received via last-hop router SHOULD ignore any mtrace2 Request received via
multicast. multicast.
10.5. First Hop Router 10.5. First Hop Router
The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default
multicast group for IPv4 mtrace responses, in order to support mtrace multicast group for old IPv4 mtrace (v1) responses, in order to
queriers that are not unicast reachable from the first-hop router. support mtrace queriers that are not unicast reachable from the
However, mtrace2 does not reserve any IPv4/IPv6 multicast addresses first-hop router. However, mtrace2 does not reserve any IPv4/IPv6
for mtrace2 responses. Every mtrace2 response is sent to the unicast multicast addresses for mtrace2 Replies. Every mtrace2 Reply is sent
address specified in the Destination Address field of the mtrace2 to the unicast address specified in the Mtrace2 Client Address field
Query header. of the mtrace2 Query header.
10.6. Broken Intermediate Router 10.6. Broken Intermediate Router
A broken intermediate router might simply not understand mtrace2 A broken intermediate router might simply not understand mtrace2
packets, and drop them. The querier would then get no response at packets, and drop them. The querier would then get no Reply at all
all from its mtrace2 requests. It should then perform a hop-by-hop from its mtrace2 Requests. It should then perform a hop-by-hop
search by setting the number of responses field until it gets a search by setting the number of hops field until it gets a Reply
response (both linear and binary search are options, but binary is (both linear and binary search are options, but binary is likely to
likely to be slower because a failure requires waiting for a be slower because a failure requires waiting for a timeout).
timeout).
10.7. Mtrace2 Termination 10.7. Mtrace2 Termination
When performing an expanding hop-by-hop trace, it is necessary to When performing an expanding hop-by-hop trace, it is necessary to
determine when to stop expanding. determine when to stop expanding.
10.7.1. Arriving at source 10.7.1. Arriving at source
A trace can be determined to have arrived at the source if the A trace can be determined to have arrived at the source if the
Incoming Interface of the last router in the trace is non-zero, but Incoming Interface of the last router in the trace is non-zero, but
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10.7.4. Traceroute shorter than requested 10.7.4. Traceroute shorter than requested
If the trace that is returned is shorter than requested (i.e. the If the trace that is returned is shorter than requested (i.e. the
number of response blocks is smaller than the "# hops" field), the number of response blocks is smaller than the "# hops" field), the
trace encountered an error and could not continue. trace encountered an error and could not continue.
10.8. Continuing after an error 10.8. Continuing after an error
When the NO_SPACE error occurs, as described in Section 9.3, the When the NO_SPACE error occurs, as described in Section 9.3, the
multicast routers sends back the mtrace2 Response to the address multicast routers sends back the mtrace2 Reply to the address
specified in the Destination Address field in the mtrace2 Query specified in the Mtrace2 Client Address field in the mtrace2 Query
header. In this case, the mtrace2 client may receive multiple header. In this case, the mtrace2 client may receive multiple
mtrace2 responses from different routers (along the path). After the mtrace2 Replies from different routers (along the path). After the
client receives multiple mtrace2 Response messages, it integrates client receives multiple mtrace2 Reply messages, it integrates (i.e.
(i.e. constructs) them as a single mtrace2 Response message. constructs) them as a single mtrace2 Reply message.
If a trace times out, it is likely to be because a router in the If a trace times out, it is likely to be because a router in the
middle of the path does not support mtrace2. That router's address middle of the path does not support mtrace2. That router's address
will be in the Previous-hop router field of the last entry in the will be in the Previous-hop router field of the last entry in the
last response packet received. A client may be able to determine last response packet received. A client may be able to determine
(via mrinfo or SNMP [11][13]) a list of neighbors of the non- (via mrinfo or SNMP [11][13]) a list of neighbors of the non-
responding router. If desired, each of those neighbors could be responding router. If desired, each of those neighbors could be
probed to determine the remainder of the path. Unfortunately, this probed to determine the remainder of the path. Unfortunately, this
heuristic may end up with multiple paths, since there is no way of heuristic may end up with multiple paths, since there is no way of
knowing what the non-responding router's algorithm for choosing a knowing what the non-responding router's algorithm for choosing a
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contrast to PIM-SM, RP always has the state to trace. contrast to PIM-SM, RP always has the state to trace.
A Designated Forwarder (DF) for a given RPA is in charge of A Designated Forwarder (DF) for a given RPA is in charge of
forwarding downstream traffic onto its link, and forwarding upstream forwarding downstream traffic onto its link, and forwarding upstream
traffic from its link towards the RPL (Rendezvous Point Link) that traffic from its link towards the RPL (Rendezvous Point Link) that
the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along
the path. the path.
11.3. PIM-DM 11.3. PIM-DM
Routers running PIM Dense Mode do not know the path packets would Routers running PIM Dense Mode [15] do not know the path packets
take unless traffic is flowing. Without some extra protocol would take unless traffic is flowing. Without some extra protocol
mechanism, this means that in an environment with multiple possible mechanism, this means that in an environment with multiple possible
paths with branch points on shared media, mtrace2 can only trace paths with branch points on shared media, mtrace2 can only trace
existing paths, not potential paths. When there are multiple existing paths, not potential paths. When there are multiple
possible paths but the branch points are not on shared media, the possible paths but the branch points are not on shared media, the
previous hop router is known, but the last-hop router may not know previous hop router is known, but the last-hop router may not know
that it is the appropriate last hop. that it is the appropriate last hop.
When traffic is flowing, PIM Dense Mode routers know whether or not When traffic is flowing, PIM Dense Mode routers know whether or not
they are the last-hop forwarder for the link (because they won or they are the last-hop forwarder for the link (because they won or
lost an Assert battle) and know who the previous hop is (because it lost an Assert battle) and know who the previous hop is (because it
won an Assert battle). Therefore, mtrace2 is always able to follow won an Assert battle). Therefore, mtrace2 is always able to follow
the proper path when traffic is flowing. the proper path when traffic is flowing.
11.4. IGMP/MLD Proxy 11.4. IGMP/MLD Proxy
When an mtrace2 Query packet reaches an incoming interface of IGMP/ When an mtrace2 Query packet reaches an incoming interface of IGMP/
MLD Proxy [8], it puts a WRONG_IF (0x01) value in Forwarding Code of MLD Proxy [8], it puts a WRONG_IF (0x01) value in Forwarding Code of
mtrace2 standard response block (as in Section 6.14) and sends the mtrace2 standard response block (as in Section 6.14) and sends the
mtrace2 response back to the Destination Address. When an mtrace2 mtrace2 Reply back to the Mtrace2 Client Address. When an mtrace2
Query packet reaches an outgoing interface of IGMP/MLD proxy, it is Query packet reaches an outgoing interface of IGMP/MLD proxy, it is
forwarded through its incoming interface towards the upstream router. forwarded through its incoming interface towards the upstream router.
11.5. AMT 11.5. AMT
AMT [9] provides the multicast connectivity to the unicast-only AMT [9] provides the multicast connectivity to the unicast-only
inter-network. To do this, multicast packets being sent to or from a inter-network. To do this, multicast packets being sent to or from a
site are encapsulated in unicast packets. When an mtrace2 query site are encapsulated in unicast packets. When an mtrace2 Query
packet reaches an AMT pseudo-interface of an AMT gateway, the AMT packet reaches an AMT pseudo-interface of an AMT gateway, the AMT
gateway encapsulats it to a particular AMT relay reachable across the gateway encapsulats it to a particular AMT relay reachable across the
unicast-only infrastructure. Then the AMT relay decapsulates the unicast-only infrastructure. Then the AMT relay decapsulates the
mtrace2 query packet and forwards the mtrace2 request to the mtrace2 Query packet and forwards the mtrace2 Request to the
appropriate multicast router. appropriate multicast router.
12. Problem Diagnosis 12. Problem Diagnosis
12.1. Forwarding Inconsistencies 12.1. Forwarding Inconsistencies
The forwarding error code can tell if a group is unexpectedly pruned The forwarding error code can tell if a group is unexpectedly pruned
or administratively scoped. or administratively scoped.
12.2. TTL or Hop Limit Problems 12.2. TTL or Hop Limit Problems
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limit) threshold) over all hops, it is possible to discover the TTL limit) threshold) over all hops, it is possible to discover the TTL
or hop limit required for the source to reach the destination. or hop limit required for the source to reach the destination.
12.3. Packet Loss 12.3. Packet Loss
By taking two traces, it is possible to find packet loss information By taking two traces, it is possible to find packet loss information
by comparing the difference in input packet counts to the difference by comparing the difference in input packet counts to the difference
in output packet counts for the specified source-group address pair in output packet counts for the specified source-group address pair
at the previous hop. On a point-to-point link, any difference in at the previous hop. On a point-to-point link, any difference in
these numbers implies packet loss. Since the packet counts may be these numbers implies packet loss. Since the packet counts may be
changing as the mtrace2 query is propagating, there may be small changing as the mtrace2 Query is propagating, there may be small
errors (off by 1 or 2 or more) in these statistics. However, these errors (off by 1 or 2 or more) in these statistics. However, these
errors will not accumulate if multiple traces are taken to expand the errors will not accumulate if multiple traces are taken to expand the
measurement period. On a shared link, the count of input packets can measurement period. On a shared link, the count of input packets can
be larger than the number of output packets at the previous hop, due be larger than the number of output packets at the previous hop, due
to other routers or hosts on the link injecting packets. This to other routers or hosts on the link injecting packets. This
appears as "negative loss" which may mask real packet loss. appears as "negative loss" which may mask real packet loss.
In addition to the counts of input and output packets for all In addition to the counts of input and output packets for all
multicast traffic on the interfaces, the response data includes a multicast traffic on the interfaces, the response data includes a
count of the packets forwarded by a node for the specified source- count of the packets forwarded by a node for the specified source-
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14.2. Traffic Rates 14.2. Traffic Rates
Mtrace2 can be used to discover what sources are sending to what Mtrace2 can be used to discover what sources are sending to what
groups and at what rates. If this information is a secret, mtrace2 groups and at what rates. If this information is a secret, mtrace2
may be restricted at the border of your domain, using the may be restricted at the border of your domain, using the
ADMIN_PROHIB forwarding code. ADMIN_PROHIB forwarding code.
14.3. Limiting Query/Request Rates 14.3. Limiting Query/Request Rates
Routers should limit mtrace2 queries and requests by ignoring the Routers should limit mtrace2 Queries and Requests by ignoring the
received messages. Routers MAY randomly ignore the received messages received messages. Routers MAY randomly ignore the received messages
to minimize the processing overhead, i.e., to keep fairness in to minimize the processing overhead, i.e., to keep fairness in
processing queries. processing queries. The rate limit is left to the router's
implementation.
15. Acknowledgements 15. Acknowledgements
This specification started largely as a transcription of Van This specification started largely as a transcription of Van
Jacobson's slides from the 30th IETF, and the implementation in Jacobson's slides from the 30th IETF, and the implementation in
mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve
Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original
multicast traceroute client, mtrace (version 1), has been implemented multicast traceroute client, mtrace (version 1), has been implemented
by Ajit Thyagarajan, Steve Casner and Bill Fenner. by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the
"S" bit to allow statistics for a source subnet is due to Tom
The idea of the "S" bit to allow statistics for a source subnet is Pusateri.
due to Tom Pusateri.
For the mtrace version 2 specification, extensive comments were For the mtrace version 2 specification, extensive comments were
received from Ronald Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Pekka received from Ronald Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Pekka
Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and Cao Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and Cao
Wei. Wei.
16. References 16. References
16.1. Normative References 16.1. Normative References
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[12] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", [12] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
RFC 2863, June 2000. RFC 2863, June 2000.
[13] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB", [13] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB",
RFC 5132, December 2007. RFC 5132, December 2007.
[14] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro, [14] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro,
"The Generalized TTL Security Mechanism (GTSM)", RFC 5082, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082,
October 2007. October 2007.
[15] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent
Multicast - Dense Mode (PIM-DM): Protocol Specification
(Revised)", RFC 3973, January 2005.
Authors' Addresses Authors' Addresses
Hitoshi Asaeda Hitoshi Asaeda
Keio University Keio University
Graduate School of Media and Governance Graduate School of Media and Governance
Fujisawa, Kanagawa 252-8520 Fujisawa, Kanagawa 252-0882
Japan Japan
Email: asaeda@wide.ad.jp Email: asaeda@wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~asaeda/ URI: http://www.sfc.wide.ad.jp/~asaeda/
Tatuya Jinmei Tatuya Jinmei
Internet Systems Consortium Internet Systems Consortium
Redwood City, CA 94063 Redwood City, CA 94063
US US
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